1. Field of the Invention
The present invention relates generally to an AE/AF solid-state imaging apparatus, and more particularly to a passive type AE/AF solid-state imaging apparatus preferably used for a lens shutter compact camera. The present invention further relates to a camera using the AE/AF solid-state imaging apparatus.
2. Related Background Art
There has hitherto been a photometric/ranging solid-state imaging apparatus disclosed in U.S. Pat. No. 5,302,997 as an auto-focus (AF) sensor incorporating a photometric (AE: Auto-Exposure)function for a lens shutter compact camera. FIG. 7 shows a schematic plane layout of this solid-state imaging apparatus. Referring to FIG. 7, there are shown a photometric sensor array 30, a photometric center segment 2, photometric (AE) inner segments 34A to 34D, photometric outer segments 36A to 36D, photometric (AE) sensor arrays 40 and 42, pixels 441-n to 461-n, an Si semiconductor substrate 50, region sizes H and W of the photometric region, and a length D of base line.
The present sensor involves using two pieces of linear sensors such as the AF sensor array 40 and the AF sensor array 42 in order to perform ranging based on a detection of a phase difference. An AF sensitivity indicating a ranging accuracy can be given by:
AF sensitivity=Dxc3x97f/P
where P is a pixel pitch, and f is a focal length of an AF image forming lens. At the present, a solid-state imaging apparatus is actualized, wherein this AF sensitivity is on the order of 5000. If the pixel pitch is on the order of 10 xcexcm and the lens focal length is several millimeters (mm), the length D of base line is 5 mm to 8 mm. Therefore, it follows that there exists an ineffective region between the AF sensor array (linear sensor) 40 and the AF sensor array (linear sensor) 42. As the AE sensor 30 is provided, however, the semiconductor substrate can be effectively utilized. Further, the AE sensor and the AF sensor are formed on one chip, thereby contributing to actualize both downsizing of the camera and a reduction in cost.
FIG. 8 is a sectional view of a structure of a region, taken along the line 8xe2x80x948 in FIG. 7. For an explanatory convenience, however, the photodiodes of the AF sensor and the AE sensor are illustrated in a way that reduces the number of these photodiodes. Referring to FIG. 8, there are sown an N type Si substrate 71, an N type epitaxial layer 72, a P type well (PWL) 73, an N+ type impurity diffusion region 74, a thin oxide film 75, a thick oxide film (LOCOS) defined as an element separation region, an AL wire 77, and an inter-layer insulation film 78. The PWL 73 and the N+ type impurity diffusion region 74 form a PN-junction photodiode. When the light enters the photodiodes of the AE sensor region and of the AF sensor region, a photoelectric conversion occurs in the semiconductor, wherein couples of electron holes are generated. The holes (each indicated by a black circle xe2x97xaf in FIG. 8) among those are discharged to GND via the PWL 73, while the electrons (each indicted by a while circle ◯ in FIG. 8) are accumulated in the floating N+ type impurity diffusion region 74 in the AE sensor region and in the floating N+ type impurity diffusion regions 74 in the AF sensor regions. The electrons gathered in these N+ type impurity diffusion regions are converted in voltage by an unillustrated amplifier element, thereby generating AE signals and AF signals.
The AF system utilized generally in the camera is classified roughly into an active type and a passive type. The active type utilizes infrared reflection rays from an object by projecting the infrared-rays upon the object from an infrared-ray projection apparatus installed into the camera, and has such a characteristic that the auto-focusing (AF) can-be performed even in a completely dark place. While on the other hand, the active type has a weak point that an object located at a far distance beyond a reachable range of the infrared-rays can not be auto-focused (AF). By contrast, the passive type, unlike the active type, utilizes a luminance signal itself of the object and therefore has no limit of distance. The passive type has, however, a weak point that the object can not be auto-focused (AF) if a luminance of the object is low. To overcome this weak point of the passive type, at the present, there is actualized an AF auxiliary light system for projecting auxiliary light when the luminance is low. Human eyes sense the auxiliary light, if visible, to be glaring. It is therefore considered desirable that the auxiliary light be near infrared-rays. For attaining this, it is desirable that the characteristic of the spectral sensitivity of the AF sensor has a peak sensitivity in the near infrared-region. The majority of actual products, however, use not the near infrared-rays but red-color light as the auxiliary light, which contains a near infrared-component having a peak at 600 to 700 nm.
In the aforementioned example of the prior art, however, the photodiodes in the AF sensor regions and the photodiode in the AE sensor region are formed in the same well, and hence a problem is that the AF sensor and the AE sensor can not be set respectively to optimal spectral sensitivity characteristics. Especially the AE sensor, if sensitive to the infrared-rays, comes to have a large photometric error due to a difference between color temperatures, and hence visual sensitivity correction filters are required of an optical system. This design raises the costs for the camera and brings about an increase in size thereof and is therefore difficult to be adopted in a compact camera. Accordingly, in the conventional photometric/ranging solid-state imaging apparatus for the compact camera, the spectral sensitivity of the AF sensor had no alternative but to match with the AE sensor.
It is an objective of the present invention to actualize an AE/AF solid-state imaging apparatus in which an AE sensor and an AF sensor respectively have spectral sensitivity characteristics optimal to their objective functions. It is another objective of the present invention to actualize a reduction in the number of visual sensitivity correction filters of an optical system.
To accomplish the above objectives, the present invention""s solid-state imaging apparatus comprises an AF photoelectric converting element for performing auto-focusing, and an AE photoelectric converting element for executing a photometric process of a photographing region, the AF photoelectric converting element and the AE photoelectric converting element being integrated on a same semiconductor substrate, wherein a spectral-sensitivity characteristic of the AF photoelectric converting element is different from a spectral sensitivity characteristic of said AE photoelectric converting element.
Further, in the present invention""s apparatus, it is desirable that a peak wavelength of the spectral sensitivity characteristic of the AE photoelectric converting element (AE sensor) is in the vicinity of 500 nm, while a peak wavelength of the spectral sensitivity characteristic of the AF photoelectric converting element (AF sensor) is 650 to 700 nm a sensitivity sufficient for a near infrared-ray region be provided. In this case, the spectral sensitivity characteristic of the AE sensor becomes similar to a human visual sensitivity characteristic, and besides the infrared sensitivity can be decreased. It is therefore possible to reduce a photometric error due to the color temperatures, and the visual sensitivity correction filters become unnecessary. Moreover, the peak wavelength of the spectral sensitivity characteristic of the AF sensor is widened to the near infrared region, whereby an AF operable range can be expanded owing to the enhanced sensitivity of the AF sensor and the auxiliary light.